Process for magnetic reduction of iron ore



June 22, 1965 R, E, K|NG 3,190,744

PROCESS FOR MAGNETIC REDUCTION OF IRON ORE Filed Jan. 9, 1963 5Sheets-Sheet l @i f3 18-` P27 sa /os 5oz /os F550 "jf g3 pas/Afef P --10,23 Il j/ June 22, 1965 R. E. KING 3,190,744

PROCESS FOR MAGNETIC REDUCTION OF IRON ORE Filed Jan. 9. 1963 3Sheets-Sheet 2 TYP/au cam/f F02 Pgs/.s nwcf ro /J/,e How o/vz y @ffm/xgaJune 22, 1965 R. E. KING 3,190,744

PRocEss Fon MAGNETIC REDUCTION OF IRON ORE Filed Jan. 9, 1965 3sheets-sheet 3 Pfff/aar Afm/cf com 57 65 jf; W

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United States Patent O 3,19%,74-4 PRGCESS FR MAGNETEC REDUCTN F IRUN GRERichard E. King, Birmingham, Ala., assigner to Northern Naturai GasCompany, maha, Nehr., a corporation of Delaware, and W. S. MooreCompany, Duluth, Minn.,

a corporation of Minnesota Filed `ian. 9, 1963, Ser. No. 250,386 14ICiaims. (Cl. 75-26) This is a continuation-impart of the presentinventors applications S.N. 89,984 tiled February 17, 1961, and nowabandoned, and S.N. 113,854, filed May 3l, 1961.

This invention relates generally to a process for reducing smallparticle size ferruginous ore materials ina gaseous suspension and moreparticularly to a process for reducing a ferruginous ore material,having at least a portion of its iron content in the form ofnon-magnetic compounds, to convert a major portion of the non-magneticcompounds to magnetite.

In the accompanying diagrammatic drawings:

FIGURE l is a flow sheet illustrating an embodiment of a process inaccordance with the present invention;

FIGURE 2 is a chart showing a graphic representation that the gaspressure developed at the bottom of an upwardly extending pipe by theliow of solids is directly proportional tothe length of the pipe and thepressure developed increases with the increasing rate of solids ow anddecreasing pipe diameter; Y

FIGURE 3 is a liow sheet illustrating the complete treatment of thematerials in a multi-stage system including one embodiment of a processin accordance with the present invention;

FIGURE 4 is an equilibrium diagram showing the wide l range oftemperatures and concentrations of the reducing gases which may beemployed; and

FIGURE 5 is a flow sheet illustrating another embodiment of a process inaccordance with the present invention.

As is well known in the art to which my invention relates, there aremany low-grade ores, such as Mesabi slaty ore, which cannot be smeltedby the conventional type blast furnace ybecause the ore contains silica,alumina and other compounds (collectively called gangue) and the ganguecauses the generation of a large volume of slag which increases the heatrequirement in the furnace and lowers the yield of metallic iron. `Also,such ores are soft whereby upon handling or shipment, the oredisintegrates into small particles which are unsatisfactory for use inthe blast furnace. Furthermore, the relatively low content of iron insuch ores requires the shipment and handling of almost three parts byweight of ore to yield one part by weight of metallic iron.

When ore is magnetic, the quality of the ore can be improved by magneticseparation of the iron oxide from the gangue. There are large quantitiesof iron-bearing, low-grade ferruginous ores now available which couldconstitute a great potential source of iron, except for the fact thatthese low-grade ores occur largely as the oxide hematite (FezOa) or ashydrated oxides such as goethite or limonite, which in theirnaturally-occurring state are not adapted for magnetic separation in theusual manner. By roasting these iron oxides in a reducing atmosphere,the non-magnetic oxides can be converted into magnetite (Fe3O4) which isseparable from a large part of the gangue by magnetic separation in amanner well understood in the art. The reducing gases usually employedare carbon monoxide (CO), hydrogen (H2) or mixtures of these two gases.The gases are generally used in a mixture of other gases which resultfrom the partial combustion of fuel, such as natural gas, oil, coal orthe like.

3,190,744 Patented June 22, 1965 This mixture of gases Valso containsother products of combustion including carbon dioxide (CO2) and water(H2O). t

Generally, a process in accordance with the present invention comprisesthe introduction of nely ground ferruginous ore material into anupwardly moving stream of pre-heated reducing gases free of uncombinedoxygen, having a temperature subjacent the fusion point of the orematerial and having sufficient velocity to maintain all the variousparticle sizes in suspension and to carry the particles through areducing zone wherein the desired reduction takes place. Inrthe processof the present invention a number of factors must be controlled foroptimum results, as will be set forth subsequently.

The simplified reaction of the reducing gas with the non-magnetic ironoxide may be represented by the following:

Due to the fact that these reactions are reversible, the accumulation ofthe gaseous products of reaction effect the rate of the reaction.

Where intimate contact of the reducing gas and the solid iron oxide ismaintained at elevated temperatures, the reduction of the iron contentof the ore from hematite to magnetite proceeds rapidly. Generally, thesurfaces of large and small particles of ore and the interior of smallparticles are readily contacted by the reducing gases and the gaseousreaction products are easily removed so that reduction of oxides solocated takes place rapidly. On the other hand, the iron oxides on theinterior of a large particle of ore are not reduced as quickly becausethe reducing gas must diffuse through a greater volume of solid materialbefore it contacts the iron oxide, and because the resulting gaseousreaction products must then diffuse outwardly through the greater volumeof solid material to escape from the reaction area and be replaced byreducing gas so that the reaction may continue. Thus, the time requiredto reduce a particle a given amount varies with the particle size,generally in linear relation thereto.

It is desirable that ore particles of various sizes be re` duceduniformly.

In accordance with the present invention, ore particles are introduceddownwardly into a rising stream of reducing gases, at a venturi, so thatthe ore particles have a downward velocity component. In order that thedownward velocity of the particles be proportional to a function of theparticle size, the particles are allowed to fall freely beforeintroduction into the reducing gas whose upward velocity should bemaintained at a rate sutlicient to offset the downward velocity of thelargest particle at the time of introduction and to convey it upwardly.The linal upward velocity of any particle, so handled, depends upon thediiference between the upward gas velocity and the downward velocity fora freely falling particle which is generally proportional to a functionof the particle size. Thus, the time a particle will spend in thereduction zone depends upon: its downward velocity at the time ofintroduction which, herein, is the downward velocity of a freely fallingparticle which is a function of the particle size; and the upward gasvelocity.

Because the times required to reduce various particle sizes a uniformamount are dependent upon the respective particle sizes and because, inaccordance with the present invention, the time a particle will spend inthe re ducing zone is dependent upon velocities which are functions ofthe particle size, it is possible to achieve substantially uniformreduction among all particle sizes even when a relatively wide range ofparticle sizes are being reduced together.

Generally, the upward velocity of a reducing gas can be controlled toassure a predetermined reduction of the largest particle suspendedtherein but, if this is the only control exercised, the extent ofreduction will not` be s ubstantially uniform over the entire range ofparticle sizes when the range of sizes varies considerably and there aresubstantial amounts of each of alarge number of different particle sizesin the range. However, substantially uniform reduction of differentparticle sizes can be obtained when the particles are introduceddownwardly and have an initial downward velocity component as described.

The reduction of hematite ore is typical of the reduction of the variousnon-magnetic ferruginous ores. This reduction reaction will occur over awide range of temperatures and concentrations of the reducing gas, asshown in the equilibrium diagram in FIGURE 4 of the drawing. At theright side of the diagram in FIGURE 4 of the drawing is shown an arearepresenting the temperature and gas compositions which result in theproduction of magnetite. Any combination of conditions within the areashown may be employed to produce magnetite. The diagram in FIGURE 4 isfor a gas consisting essentially of carbon monoxide and carbon dioxide.The temperature and the ratio of carbon monoxide to the sum of carbonmonoxide plus carbon dioxide in the reducing gases must be maintained ata value below line Y-Z and to the right of the line X-Y respectively.That is, a relatively low ratio of CO2CO-l-CO2 and a relatively hightemperature will normally produce magnetite, as is shown in FIGURE 4.However, if the ratio of carbon monoxide to the sum of carbon monoxideplus carbon dioxide in the reducing gases is too low, the conditions areoxidizing for magnetite, and hematite may exist. On the other hand,where the temperature and the ratio of carbon monoxide to the sum ofcarbon monoxide plus carbon dioxide in the reducing gases are maintainedat a value above the line W-Y-Z, the conditions are reducing formagnetite and wustite may be formed, which is a nonmagnetic material.Temperature conditions and gas ratios below and to the left of lineW-Y-X are fully reducing and will produce metallic iron.

A similarily shaped equilibrium diagram would exist where the reducinggases contain H2 and H2O. Generally, the ratio of H2 to Hzi-i-HgO andthe temperature must both be controlled to provide conditions which willreduce hematite to magnetite without overly reducing to wustite ormetallic iron.

A mixture of CO and CO2 and a mixture of HZ and H2O are both obtainedtogether by the partial combustion of natural gas with air. mixture andHZ-HZO mixture exist in the same gas, other factors become significantwhich are not present when only one of the two gas mixtures is reliedupon for reducing hematite. For example, a ratio of CO to CO-l-COz whichwould overly reduce in the absence of H2 and H2O may not do so in thepresence of H2 and H2O in certain ratios, and vice versa.

Thus, if the ratios of H2 to HTI-H2O and CO to CO-l-COZ are each in anarea on their respective equilibrium diagrams which will producemagnetite at the prevailing temperature, there is no difculty inmaintaining magnetite. If the ratio of H2 to HLA-H2O is in an area whichwill overly reduce magnetite at the prevailing temperature, magnetitecan still be maintained and over reduction be prevented because thereare ratios of CO to CO-l-COz which will enable the production ofmagnetite in the presence of over-reducing ratios of H2:H2|-H2O. Morespecilically, referring to FIGURE 4, if the CO to CO-I-CO2 ratio issuiciently below and to the right of the line X-Y-Z at the particularreaction temperature, and the ratio of H2 to HTI-H20 is relatively high(in an area which would produce wustite if the gas contained only amixture of H2-H2O), then overreduction would probably not occur andmagnetite would probably be produced.

When both the CO-COZ r To prevent over-reduction, when the two gasmixtures are used together, it is necessary to maintain either the ratioof COzCO-I-CO2 or the ratio of HzzHz-l-HZO below the critical valuewhich will enable the production of magnetite when the other ratio isover-reducing. One method of lowering these ratios is to increase theextent of partial combustion of the fuel (e.g., natural gas). However,this method generates too much heat, which is undesirable because it maycause fusion of the ore particles; and it requires a relatively largequantity of fuel to yield the quantity of reducing gases necessary forthe amount of iron ore to be reduced.

In accordance with the present invention, fuel is burned with the leastquantity of air necessary to obtain the desired quantity of reducinggases. The ratios of CO:CO2 and H22H2O are then adjusted by adding CO2and/or water vapor until the resulting reducing gas contains a mixtureof both CO-COz and P12-H2O which, together, will maintain magnetite andprevent over reduction at the temperature prevailing.

Another factor to be considered is that the reduction reactions occur ina rising stream of gas which is moving faster upwardly than the oreparticles being reduced. Accordingly, at any location along the upwardlyextending reduction path there will be a greater ratio of reducing gasto non-reducing gas (e.g., CO to CO2) than would be the case if the oreparticles and the gas were moving at the same speed. Conversely, becausethe ore particles are moving at slower speeds than the gas, at anylocation along the upwardly extending reduction path an ore particlewhich is moving substantially slower than the gas will have undergonemore reduction than it would have undergone had it moved at the samespeed as the gas. Both of these factors tend to permit over-reduction.

To prevent over-reduction under these circumstances, the gas, uponinitial commingling with the ore particles, should have a compositionincluding ratios of COzCO-i-COz and H21H2-l-H2O which, for theprevailing temperature, will prevent over-reduction along the upwardlymoving reduction path and which will assure that ore particles leavingthe reduction zone will be magnetite rather than wustite or metalliciron.

Because some CO2 and some H2O will be generated along the reductionpath, and because over-reduction is not a problem at initial portions ofthe reduction path (inasmuch as the ore is virtually all hematite atsaid initial portions) the ratios of COrCO-l-COZ and HzzHz-l-HZO, uponinitial commingling, need not neces- -sarily be those which willmaintain magnetite. However, at subsequent portions of the reductionpath these ratios must be such that there is enough CO2 and/ or H2O(both initially added and subsequently generated) to preventover-reduction and maintain magnetite.

At the end of the reduction path, the particles are separated from thegas. The gas is hot and may be recycled to earlier stages of the `systemfor preheating purposes.V The gas may also be mixed with gas from thecombustion furnace to increase the CO2 and H2O in the gas mixtureentering the reduction path.

Referring now to the drawings for a better understanding of myinvention, I show a two-stage system in FIG- `URE l which comprises afirst upwardly extending riser 10 and a second upwardly extending riser11. A gas inlet 12 is provided at the lower end of riser 10 while theupper end of riser 10 communicates with a cyclone separator 13 whichseparates the gas from the solid particles. The Vsolid particles aredischarged from cycline separator 13 through a discharge conduit 14.Communicating with the gas discharge of separator 13 is a downwardlyextending conduit 17 which in turn communicates with the lower end ofsecond riser 11 whereby the stream of gases indicated by the dottedarrow 18 are conveyed upwardly through second riser 11. The upper end ofriser 11 cornmunicates with a cyclone separator 19 having a gas out-`let 2l and an outlet 22 for discharging solid particles.

The lower ends of risers 10 and 11 are provided with venturi throats 23and 24 respectively. Communicating with venturi 24 is a downwardlyextending inlet conduit 25 for supplying the small particle sizematerials to be roasted. The materials thus introduced through conduit26 are conveyed upwardly by the upwardly moving stream of gases, theflow of the solid particles being indicated by the solid arrows 2.7. Asthe concurrently flowing stream of gas and solid particles pass throughseparator 19, the gases are discharged through outlet 21 while the solidparticles are discharged downwardly through outlet 22.

Communicating with solid discharge outlet 22 is the upper end of adownwardly extending conduit 28. The lower end of conduit 28communicates with venturi 23 whereby the solid particles are introducedinto the lower end of rst riser 10.

From the foregoing description, the operation of the process illustratedin FIGURE 1 will be readily understood. Preheated, hot reducing gasesare continuously introduced through inlet 12 at venturi 23 whereby theyow upwardly through riser 10 and separator 13 and then flow downwardlythrough conduit 17 to venturi 24 at the lower end of second riser 11.After passing through venturi throat 20.1, the gaseous stream passesupwardly through riser 11 and is finally discharged through outlet 21or" separator 19. The solid materials are fed into venturi 2d throughconduit 2.6 whereby they are conveyed upwardly and flow concurrentlywith the stream of gas to separator 19. The solid particles aredischarged from separator 19 through outlet 22 into yconduit 2Swhereupon the solids are introduced into venturi 23 of riser liti. Thesolid particles then flow upwardly and concurrently with the hotreducing gases introduced through inlet 12 to separator 13. The solidparticles are discharged from separator 13 through outlet 14. Thevolumev of gases introduced into riser 1@ and the size of riser 1@ issuch that the velocity of the gas .stream will suspend theine particlesize materials and convey them to separator 13. This velocity isdependent largely upon the particle size and density of the ne ore. lnactual practice, I have found that a velocity greater than l feet persecond is usually required to prevent particles of ferruginous ore .fromsettling out of the gas stream due to the forces of gravity;

It will thus be seen that the solid particles and reducing gas flowconcurrently as they pass upwardly through risers 1@ and 11 whereby thesolid particles are suspende-d in the moving gases. However, the overallow of the solids is countercurrent to the flow of gases. That is to say,the solid particlesare introduced into the lower end of second riser 11and are then passed through first riser 11D before being discharged.Accordingly, second riser 411 serves as a preheater while first riserserves` as a reactor. Because down ilow of solid materials in conduitA28 is essential to the maintenance of pressure balance and properdirection of gas flow, the introduction of solids at 26 must be startedat a relatively low rate and -gradually increased to the properoperating level. Also,

if desired, a suitable Valve may be provided in conduit Z8 whereby theow of gas through conduit 2S is restrained until the system is `placed.in operation. That is, valve 25 would be gradually moved to openposition after a solids feed rate has been established. Also, solidsdischarge outlet 14 is connected to a solids discharge system whichrestricts the flow of gas into and out of the system. As the solids owupwardly concurrently with the gas stream, gravity restrains upwardmovement of the larger particle size materials more than it restrainsupward movement of the smaller particle size materials `whereby thelarger particle size materials are subjected to longer exposure to thehot gases thereby bringing about the required minimum amount ofreduction of the larger particle size materials.

Unless counteracted, the gas introduced at inlet 12 will tend to passupwardly through solids downcomer 28 to separator 19, .therebyshort-circuiting the reaction zone and greatly lowering the separatingefficiency of separator 19. That is, because of frictional losses in thesystem, the gas at the inlet will be at a higher pressure than the gaswithin separator 19, unless counter-acted. The desired flow of gas isthrough venturi 23 and upwardly through first riser 1t) to separator 13and then downwardly through conduit 17 .to the lower end of second riser11 where the gas ows upwardly therethrough and is finally dischargedthrough outlet 21. This problem cannot be solved by providing amechanical air-lock device, such as a rotary feeder or `a gravitytrickle valve due to the fact that such devices would not besatisfactory for use at temperatures employed for the reduction of iron.

Proper flow of the gases and solids is provided without the use ofmechanical devices. When gas alone is flowing through the system thepressure drop of the gas flowing through the desired path in myapparatus is almost completely equalled by the venturi pressure changeso that essentially no pressure exists Ito cause flow of gas upwardlythrough the conduit or solids downcomer 28. In actual practice, whensolids are being conveyed by gas in the illustrated system, the pressuredrop through the desired path is increased while the differential ofpressure brought about by the venturi may be reduced by the presence ofsolids. By proper choice of the diameter and length of solids downcomer28, the solids failing down the solids downcomer 28 will increase thegas pressure near the bottom of the downcomer and short-circuiting ofgas, when the system `is conveying solids, can be prevented.

The pressure developed by solids falling in a standpipe is important inthe function of the illustrated multi-stage system due to the fact thatthe solid particles ow down the downcomer 28. The gas pressure developedat the bottom of a standpipe by the ow of -solids is directlyproportional to the length of the standpipe. FIGURE 2 of the drawingsshows that the pressure developed also increases with the increasingrate of solids flow and decreasing pipe diameter. The iron ore employedin obtaining the results shown in FIGURE 2 was minus 2O mesh iron ore.The curves show that the pressure devel# oped is much reduced in largerdiameter pipe, such as would be used in commercial operation. However, acompensating factor is that the resistance offered to gas flow in theriser and other parts of the system will also be reduced in largerdiameter pipes, as shown by the dashed line in FIGURE 2. Accordingly,the pressure developed by falling solids would be'equally useful in alarge commercial system to prevent upward iiow of gas through the solidsdowncomer 25. The pressure developed is indicated in FIGURE 2 by inchesof water, on the water gauge, over the length of the conduit, measuredin feet.

Referring now to FIGURE 3 of the drawings, I show the complete treatmentof the materials in a multi-stage system. The crushed ore is stored in asuitable bin 29 and is transferred to a dry-grinding system indicatedgenerally at 31 whereby the ore is pulverized and dried simultaneously.The particle size to which the ore must be crushed to effect rapidreaction is determined by the physical characteristics of the naturalore. That is, some natural ores have a porous structure which permitssome penetration of gas into the interior of the particles. T-hese oreswill reduce rapidly at a much coarser size than will an ore having adense structure. In actual practice, many ores can be reduced in theillustrated system by crushing the ores to a particle size whereby thelargest particles will pass a standard l0 mesh testing sieve. Y

The finely pulverized ore passes from the grinding system 31 to an airclassiiier 32 and then Ato a cyclone separator 33 Where exhaust gasesare removed as at 34. The pulverized ore is stored .in a bin 36 and isthen con- Veyed through a supply line 37 to an upwardly extending riser38 which communicates at its Yupper end with a cyclone separator 39. Theexhaust gases from separa-tor 39 are removed through a conduit 41 wherethey are conveyed through grinding system 31, air classifier 32 andseparator 33 whereby the gases dry the ore introduced into the grindingsystem. The fine particle size materials introduced into riser 38 thusmove concurrently and in suspension with the gaseous stream to separator39.

The gaseous stream supplied to line 38 comes from the exhaust of acyclone separator 42. The tine particle size ore materials dischargedfrom the lower end of cyclone separator 39 enter a line 43 and are thendischarged into a riser 44 which communicates the gas exhaust of acyclone separator 45 with cyclone separator 42. The upwardly movingstream of gas in riser 44 picks up the tine particle size ore materialswhereby they are suspended in the gas and conveyed concurrentlytherewith to separator 42.

Communicating with cyclone separator 45 is the upper end of riser 46.The lower end of riser 46 communicates with a line 47 which supplies thegaseous stream from a gas generator 48. Solid materials discharged fromseparator 42 are introduced into the lower end of riser 46 by a line 49whereby they move upwardly and concurrently in suspension with thegaseous stream to separator 45. The reducing gases formed in gasgenerator 48 may be provided by introducing air through a conduit 51 andnatural gas through a conduit 52 whereby they are mixed and partiallyburned in gas generator 48 prior to being introduced into riser 46. Thecomposition and temperature of the gases leaving the generator 48 may becontrolled by recycling a portion of the gaseous stream exhausted fromcyclone separator 42 (and containing CO2 and H2O) through a line 53 toair supply line 51. As an alternative embodiment H2O and/or CO2 from anoutside source may be introduced linto conduit 47 through a line 60.

The movement of the tine particle size ore materials through risers 38and 44 serves as a temperature preparation whereby the ore is preheatedprior to being introduced into riser 46 carrying the hot reducing gases.The tine particle size materials to be roasted are fed through theapparatus at a suitable rate whereby the particles are freely suspendedcompletely or fully in the reducing gases while passing through riser46. Riser 46 thus serves as a reaction zone whereby the ine particlesize materials are not only suspended in this zone but flow concurrentlywith the reducing gases to separator 45. The volume of the reducinggases introduced in riser 46 and the size of riser 46 is such that thevelocity of the gas stream will suspend the ne particle size materialsand convey them to separator 45. As the ore particles pass throughseparator 45, they are separated and are discharged into a cooler 54.

From cooler 54, the reduced or passes to suitable magnetic separatorsindicated generally at 56 whereby the magnetic materials are separatedfrom the non-magnetic materials. The magnetic ore may then pass tosuitable briquetting or pelletizing apparatus 57 in a manner wellunderstood in the art.

Another embodiment is illustrated in FIGURE and is similar in manyrespects to that illustrated in FIGURE 3. However, in addition to thetwo preheating stages consisting of separators 3-9, 42 and theirassociated downcomers and risers, and the reducing stage consisting ofseparator 45, etc., the embodiment of FIGURE 5 also includes a c-oolingstage comprising a cyclone separator 160.

Reduced ore particles leave reducing zone separator through a downcomer162 and are fed into an upwardly moving stream of gas in a riser 161.The bottom of riser 161 communicates with the top of first preheat stageseparator 39 through a conduit 141 which also communicates with aconduit 171 leading to a vent (not shown). The gases in riser 161 havepreviously passed through two preheat stages (i.e., at separators 42 and39) where much of the heat of the gases has been transferred to the ironore particles to preheat the latter. Accordingly, the gas in riser 161is substantially cooler than the reduced iron Cil ore particlesintroduced into riser 161 from downcomer 162, .and the gas will cool theiron ore particles suspended therein. Iron ore particles from coolingstage separator 16) pass downwardly through a conduit 163 to a quenchtank 165. Gases from separator 160, now substantially hotter after theexchange of heat with the ore particles, pass into a conduit 164 whichcommunicates with the bottom of riser 44, at the second preheat stage,via a blower 166 and a conduit 167.

Also communicating with the bottom of riser 44, in series, are conduits173 and 168, the latter communicating with the top of reducing stageseparator 45. Hot reaction gases pass from separator 45 through conduits168, 173 to riser 44 to assist in the preheating. Gases from conduit 168also pass through a conduit 172 into riser 46. The gases from 172 minglewith the reducing gases from furnace 48 to help adjust the CO:CO-}CO2and HgzHz-l-HzO ratios to .the desired levels, as discussed with respectto the function of conduit 53 in the embodiment of FIGURE 3.

Gases from separator 42 pass through a conduit 170 to the bottom ofriser 38, into separator 39, and from there .to cooling riser 161 viaconduit 141.

A second or preheat stage furnace 14S effects a substantial combustionof natural or combustible gas with air and feeds the resulting gasesthrough .a conduit 169 and conduit 173 into riser 44 of the secondpreheat stage. Thus, riser 44 contains a commingling of gases fromreducing separator 45, from furnace 148 and from cooling separator 160.

Because the gases in riser 44 are eventually introduced into coolingstage riser 161 (after having passed through both preheat separators 42,39 in that order), and because riser 161 conveys ore particles whichhave already been reduced, it is important that the gas introduced intoriser 161 be of a composition which will maintain a particle compositionof magnetite. Therefore, the gases in riser 161 should contain no freeoxygen and be slightly reducing, but, also, not over-reducing.

Gases such as CO2 and H2O have a higher heat capacity and permittransfer of a greater quantity of heat with a smaller volume of gas thendo gases such as CO or H2. Accordingly, it is desirable that the gasespassing through the preheat stages have as much CO2 and H2O as ispossible without creating conditions which are oxidizing to the reducedore particles in cooling riser 161 into which the gases from the preheatstages eventually ow. Some of the desired H2O and CO2 are provided bythe exhaust gases from the reducing stage (i.e., through conduits 168and 173 to preheat riser 44). Additional CO2 and H2O is provided bycombustion of fuel in furnace 148, communicating with riser 44 throughconduits 169, 173. To the extent that large quantities of heat aregenerated in furnace 148, this is acceptable during the preheat stageswhere fusion of the as yet unheated or slightly heated ore particles isnot a problem as it is in the reducing stage.

Therefore, furnace 148 is controlled to produce a gas for mixture withother gases entering riser 44 to give a composition having as high acontent of CO2 and H2O which can be tolerated and still preventoxidation of reduced ore particles in cooling riser 161.

In order to convert one pound of hematite to magnetite, approximately0.8 cubic foot of either carbon monoxide or hydrogen (dry basis, 60 F.,29.92 inches of mercury) is required. Where the reducing gas contains15% carbon monoxide or hydrogen at a temperature of approximately 1400F. and atmospheric pressure, the gas volume required for one pound ofhematite is approximately 19 cubic feet. Approximately this volume ofgas is required to suspend one pound of hematite and the other materialsassociated therewith in the natural ore.

The suspension of fine particle size materials in reducing gases ismaintained at an elevated temperature which is below the fusion point ofthe various components of the material. That is, it is desirable toprevent the par- 9 yticles from passinginto the liquid or melted stateduring the reaction.

Increasing the ytemperature increases the reaction rate. As an example,an iron ore containing 50% iron was crushed to pass a 30 mesh testingsieve. This ore was reduced in a stream of reducing gas havingapproximately 8.8% carbon monoxide.

At a temperature of approximately 1090 F., the ore was 68% reduced tomagneti-te in 3 seconds.

At a temperature of approximately 1250 F., the ore Was 82% reduced tomagnetite in 3 seconds; and,

At .approximately 1375 F., maximum reduction to magnetite was obtainedin 3 secondsg As another' example, iron ore containing 57% iron wascrushed to pass a 30 mesh sieve and was treated with the Same gascomposition listed in theexample hereinabove for 3 seconds atapproximately '1240 F. The ore was 82% reduced to magnetite in the 3seconds.

The relationsihp of the size of the tine particle size materials to thevelocity of the reducing gases is maintained at or above a value whichprevents any particles of the ore from settling out of the gaseousstream'due solely to the action of gravity.

As an example of the operation of the process, an iron ore containing43.6% iron was crushed to pass a 14 mesh testing sieve. Thisore wasreduced in a two-stage apparatus similar to that shown in FIGURE 1 inwhich the risers were of standard 1% inch pipe approximately 7 feetlong. lThe reducing gas contained 16.5% carbon monoxide and hydrogen.The measured temperature of the gas was maintained at approximately1540J F. Essentially complete reduction of the iron oxide to magnetitewas obtained at an ore rate of approximately 188 pounds per hour and agas rate of l standard (60 F., 29,92 inches of mercury) cubic feet perminute.

The foregoing describes an improved process for treating ore-likematerials, such as ferruginous ores. While the described process isparticularly adapted for use in treating ferruginous ores, it will beapparent `that it is also adaptable generally for roasting othermaterials, such as pyrite and the like. By roasting the ine particlesize materials while they are in complete suspension in the hot gases,the roasting or reduction takes place in a' minimum of time. Also, byconstructing and arranging the appartus whereby the pressure drop of gasflowing through the risers and the equipment associated therewithissubstantially equal to the change of pressure at the venturi in thefirst riser and that created by solids flowing down the solidsdowncomer, there is substantially no pressure drop across the solidsdowncomer to cause flow of gas directly from the gas inlet to theseparator associated with the second riser.

The foregoing detailed description has been given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom, as modications will be obvious to those skilled in the art.

What is claimedV is:

1. The process of treating a ferruginous ore material having a-t least aportion of its iron content in the form of non-magneticoxygen-containing compounds reducible to magnetite, said processcomprising the steps of:

providing said ore material as iinely divided particles;

providing a stream of heated gases consisting essen- 'tially of at leastone gas selected from a first group consisting of carbon monoxide (CO)and hydrogen (H2) and at least one gas selected from a second groupconsisting of carbon dioxide (CO2) and water vapor (H2O), with saidstream of gases being free of uncombined oxygen and at a temperaturebelow the fusion point of said ore material;

providing said stream of gases With a ratio of iirstgroup gases tosecond-group gases which is reducing to said ore material at saidtemperature;

introducing said stream of gases into one end of a closed,longitudinally extending reaction zone and moving the stream of gasesthrough said reaction zone;

introducing said particles of ore material into said one end of saidreaction zone with the particles having a downward velocity component atthe time of said introduction;

forming a free suspension of said particles in said stream ot gases,with said suspension moving through the reaction zone from said one endto the other end thereof;

reducing said non-magnetic oxygen-containing compounds in said particlesto magnetite, during movement of the suspension rthrough said reactionzone, to render said particles magnetic;

controlling the ratio of first-group gases to second-group gases and thetemperature of said stream of gases in the reaction zone to preventover-reduction of the ore particles to metallic iron or to wustite andto maintain magnetite at the other end of the reaction zone; separatingsaid ore particles at said other end of the reaction zone from lsaidstream of gases; the movement of said stream of gases, from the time theore particles become suspended in the stream of gases until the streamof gases reaches the other end of the reaction zone, consisting ofmovement in a direction having an upward component; and magneticallyseparating the magnetic particles from the non-magnetic particles insaid ore material, without further reduction of the ore material. Z. Theprocess of claim 1 wherein the largest of said ore particles is smallerthan a standard l() mesh.

3. The process of claim l wherein said stream of gases is heated to atemperature between 1090 F. and 1540 F. 4. VThe process of treating aferruginous ore material having at least a portion of its iron contentin the form of non-magnetic oxygen-containing compounds reducible tomagnetite, said process comprising the steps of:

providing said ore material as iinely divided particles; providing astream of heated gases consisting essentially of at least one gasselected from a first group consisting of carbon monoxide (CO) andhydrogen (H2) and at least one gas selected from a second groupconsisting of carbon dioxide (CO2) and water vapor (H2O), with saidstream of gases being free of uncombined oxygen and at a temperaturebelow the fusion point of said ore material; providing said stream ofgases with a ratio of iirstgroup gases to second-group gases which isreducing to said ore material at said temperature; introducing saidstream of gases into a closed, upwardly extending reaction zone andmoving said stream upwardly through said reaction zone; introducing saidparticles of ore material into said upwardly moving stream of gases atthe bottom of said reaction zone; forming, in said closed reaction zone,an upwardly moving free suspension of said particles in said stream ofgases; reducing said Vnon-magnetic oxygen-containing cornpounds in saidparticles to magnetite, during movement of the suspension through saidreaction zone, to render said particles magnetic; controlling the ratioof iirst-group gases to secondgroup gases and the temperature in saidstream of gases in the reaction zone to prevent over-reduction of theore particles to metallic iron or wustite and to maintain magnetite atthe top of the reaction zone; separating said ore particles at said topof the reaction zone from said stream of gases; magnetically separatingthe magnetic particles from the non-magnetic particles in said orematerial, without further reduction ofthe ore material; introducing saidore particles, before introduction thereof into said reaction zone, intoone end of a longitudinally extending, closed preheating zone;

introducing hot preheating gases into said one end of the preheatingzone, and moving said gases upwardly through the preheating zone;

forming a free suspension of said ore particles in said preheating gaseswith said suspension moving through the preheating zone from said oneend to the other end thereof;

said ore parlicles and said hot preheating gases undergoing a mutualheat transfer during movement of the suspension through said preheatingzone to provide heated ore particles and cooled gases; and separatingthe heated ore particles at said other end of the preheating zone fromsaid cooled gases;

the movement of said preheating gases, from the time the ore particlesbecome suspended in the preheating gases until the stream of gasesreaches the other end of said preheating zone, consisting of movement ina direction having an upward component;

' at least part of lthe volume of said hot preheating gases beingprovided by circulating gases from said stream of gases a-t the top ofsaid reaction zone to the one end of said preheating zone.

5. A process as recited in claim 4 wherein:

another part of the volume of said hot preheating gases is provided byeffecting combustion of combustible gases with air at a location outsidethe reaction zone, between one end of the preheating zone and the top ofsaid reaction zone, to produce a mixture of gases free of uncombinedoxygen and including at least one of said second-group gases;

and circulating said mixture of gases to the one end of the preheatingzone.

6. A process as recited in claim 4 and comprising:

controlling the ratio of said second-group gases to said iirst-groupgases in said preheating zone so that said ratio is as high as ispossible without causing oxidation of magnetite at the temperatureprevailing in the o re material separated at the other end of saidreaction zone.

7. The process of treating a ferruginous ore material having at least aportion of its iron content in the form of non-magneticoxygen-containing compounds reducible to magnetite, said processcomprising the steps of:

providing said ore material as linely divided particles in a relativelywide range of particle sizes each having a substantial amount, byweight;

providing a stream of heated gases consisting essentially of at leastone gas selected from a first group consisting of carbon monoxide (CO)and hydrogen (H2) and at least one gas selected from a second groupconsisting of carbon dioxide (COZ) and water vapor (H2O), with saidstream of gases being free'of uncombined oxygen and a temperature belowthe fusion point of said ore material;

providing said stream of gases with a ratio of firstgroup gases tosecond-group gases which is reducing to said ore material at saidtemperature;

introducing said stream of gases into one end of a closed,longitudinally extending reaction zone and moving the stream of gasesthrough said reaction zone;

introducing said particles of ore material into said one end of saidreaction zone with the particles having a downward velocity component atthe time of said introduction;

permitting said particles to fall freely, due to the action of gravityalone, until introduction thereof into the reaction zone, whereby theparticles have a downward velocity component proportional to a functionof the particle size;

forming a free suspension of said ore particles in said stream of gases,with said suspension moving through the reaction zone from sai-d one endto the other end thereof;

reducing said non-magnetic oxygen-containing cornpounds in saidparticles to magnetite, during movement of the suspension through saidreaction zone, to render said particles magnetic;

maintaining the largest of said particles in said reaction zone until ithas been reduced to the extent desired, whereby each of the particlesizes is subjected to substantially uniform reduction on the basis ofweight percent undergoing reduction;

controlling the ratio of first-group gases to secondgroup gases and thetemperature of said stream of gases in the reaction zone to preventover-reduction of the ore particles to metallic iron or to wustite andto maintain magneti-te at the other end of the reaction zone;

separating said ore particles at said other end of the reaction zonefrom said stream of gases;

the movement of said stream of gases, from the time the ore particlesbecome suspended in the stream of gases until the stream of gasesreaches the other end of the reaction zone, kconsisting of movement in adirection having an upward component;

and magnetically separating the magnetic particles from the non-magneticparticles in said ore material, without further reduction of the orematerial.

8. The process of treating a ferruginous ore material,

having at least a portion of its iron content in the form ofnon-magnetic oxygen-containing compounds reducible to magnetite, saidprocess comprising the steps of:

providing said ore material as inely divided particles;

providing a stream of heated gases consisting essentially of at leastone gas selected from a iirst group consisting of carbon monoxide CO)and hydrogen (H2) and at least one gas selected from a second groupconsisting of carbon dioxide (CO2) and water vapor (H2O), with saidstream of gases being free of uncombined oxygen and at a temperaturebelow the fusion point of said ore material;

providing said stream of gases with a ratio of firstgroup gases tosecond-group gases which is reducing to said ore material at saidtemperature;

introducing said stream of gases into one end of a closed,longitudinally extending reaction zone having a pair of ends, and movingsaid stream through said reaction zone;

introducing said particles of ore material into said moving stream ofgases at one end of said reaction zone;

forming, in said closed reaction zone, a free suspension of saidparticles and said stream of gases, and moving said suspension throughsaid reaction zone;

reducing said non-magnetic oxygen-containing compounds in said particlesto magnetite, during movement of the suspension through said reactionzone, to render said particles magnetic;

controlling the ratio of first-group gases to secondgroup gases and thetemperature in said stream of gases in the reaction zone to preventover-reduction of the ore particles to metallic iron or wustite and tomaintain magnetite at the other end of the reaction zone;

separating said ore particles at said other end of the reaction zonefrom said stream of gases;

magnetically separating the magnetic particles from the non-magneticparticles in said ore material, without further reduction of the orematerial;

introducing said ore particles, before introduction thereof into saidreaction zone, into one end of a longitudinally extending, closedpreheating zone having a pair of ends;

introducing hot preheating gases into the one end of the preheatingzone, and moving said gases through the preheating zone;

heating gases and ore particles, with the suspension moving through thepreheating zone;

said ore particles and said hot preheating gases undergoing a mutualheat transfer during movement ot` the suspension through said preheatingzone to provide heated ore particles and cooled gases;

separating the heated ore particles at the other end of the preheatingzone from said cooled gases;

ing stream of gases at one end of said reaction zone; forming, in saidclosed reaction zone, a free suspension of said particles and saidstream of gases, `with said suspension moving through the reaction zone;reducing said non-magnetic oxygen-containing compounds in said particlesto magnetite, during movement of the suspension through said reactionzone, to render said particles magnetic; controlling the ratio ofrst-group gases to secondat least part of the volume of said hotpreheating gases group gases and the temperature in said stream of beingprovided by circulating gases from said stream gases in the reactionzone to prevent over-reduction c of gases at the other end of saidreaction zone to of the ore particles to metallic iron or wustite andthe one endof said preheating zone; to maintain magnetite at the otherend of the reintroducing said magnetite-containing ore particles, actionzone;

after said separation thereof from said stream of 15 separating said oreparticles at said other end of the gases, into one end of a closedlongitudinally extendreaction zone from said stream of gases; ingcooling zone having a pair of ends; magnetically separating the magneticparticles from circulating said cooled preheating gases from said thenon-magnetic particles in said ore material, withother end of saidpreheating zone into said one end out further reduction of the orematerial; of said cooling zone, suspending said ore particlesintroducing said ore particles, before'introduction therein said cooledgases in the cooling zone, and conof into said reaction zone, into oneend of a longiveying said ore particles in suspension with saidtudinally extending, closed preheating zone having cooled preheatinggases through said cooling zone to a pair of ends; the other elldthereof, Wherehy the ore material is introducing hot preheating gasesinto said one end of Cooled and the gases are heated; the preheatingzone, and moving said gases through separating said cooled ore particlesat said other end the preheating zone;

of the COOlihg Zone from Said heated gases; forming, in said preheatingzone, a suspension of preand controlling the composition of Saidpreheating heating gases and ore particles, with the suspension gases,before introduction thereof into said cooling moving through thepreheating zone; zone, to eXcludc uncombined oxygen and to provide ao:said cre particles and said hot preheating gases undera ratio ofiirst-group gases to second group gases going a mutual heat transferduring movement of the which Will maintain magnetite at the temperaturesSuspension through the preheating zone to provide prevailing in saidcooling zone. heated ore particles and cooled gases; 9. A process asrecited in claim 8 and comprising: separating the heated ore particlesat the other end of circulating heated gases from said other end of thethe preheating zone from said cooled gases;

cooling zone to said one end of the preheating zone. at least part ofthe volume of said hot preheating gases 10- A Process as recited iuclaim s Wherein being provided by circulating gases from said streamanother part of the volume of said hot preheating gases of gases at theother end of said reaction zone to the is provided by effecting partialcombustion of comone end of said preheating zone; bustible gas With air,at a locatioI1 outside the reac- 40 another part of the volume of saidhot preheating gases tion zone between said one end of the preheatingbeing provided by effecting Combustion of com- Zone and Said Other end0f the reaction Zone, t0 bustible gases with air, at a location outsidethe reproduce a mixture of gases free 0f uricoihhirled action zonebetween one end of the preheating zone oxygen and including at least oheof said secoudand the other end of said reaction zone, to produce groupgases; amixture of hot gases free of uncombined oxygen and c1rculat1ngsaid mixture of gases to said one end and including at least one of SaidSecond-group gases; of said preheating zone. commingling said other partof said hot gases with said 11- A Process as recited irl claim 8 aridcorhPrisiug hot gases circulated from the other end of Isaidrecohtrolllug the ratio of said secoi1d-grouP gases to said action zone,before introduction of the hot gases into iirst-group gases in saidpreheating zone so that said o the preheating zone; ratio is as high asis Possible Without causing oXi d and controlling the composition ofsaid hot preheating datioii of Inagile-tite at the temperatureprevailing iii gases to exclude uncombined oxygen and provide, at theore material separated at the other end of said said other end of saidpreheating Zone, a ratio 0f reaction Zone first-group gases tosecond-group gases which will 12- The Process 0f treating a ferruglnousOre material 5,- maintain magnetite at the temperature prevailing inhaving at least a portion of its iron content in the form o the orematerial Separated at the other end of Said of non-magneticoxygen-containing compounds reducible reaction Zone. to magnetite, saidProcess comprising the steps of: 13. A process as recited in claim 12and comprising: ProVidihg Said ore material as hely diVided Particles?controlling the ratios of said second-group gases to Providing a Streamof heated gases consisting essen' l60 said rst-group gases in saidpreheating zone so that tially of at least one gas selected from a firstgroup said ratios are as high as is possible Without causing Consistingof Carbon monoxide (C0) and hydrogen oxidation of magnetite at thetemperature prevailing (H2) arid at least ohe gas selected from a secondin the ore lnaterial separated at the other end of said group consistingof carbon dioxide (CO2) and Water reaction zone Vapor (H2O), With saidstream of gases being frcc 65 14. A process for treating ore material,said process of uncombined oxygen and at a temperature below Comprisingthe steps of; the fusioh Point of said ore material; providing said orematerial as finely divided particles; Providing said stream of gasesWith a ratio of iirstproviding a stream of heated gases reactive withsaid group gases to second-group gases which is reducing ore material,said stream of gases having a temperato said ore material at saidtemperature; ture below the fusion point of said ore material;introducing said stream of gases into one end of a introducing saidstream of gases into a closed, longiclosed, longitudinally extendingreaction zone having tudinally extending reaction zone having a pair ofa pair of ends, and moving said stream through said ends, and movingsaid stream through said reaction reaction zone; zone; introducing saidparticles of ore material into said movintroducing said particles of orematerial into said moving stream of gases at one end of said reactionzone;

forming, in said closed reaction zone, a moving free suspension of saidparticles and said stream of gases;

reacting said ore material with said gases during movement of thesuspension through said reaction zone;

separating said ore particles at said other end of the reaction zonefrom said stream of gases;

introducing said ore particles, before introduction thereof into saidreaction zone, into one end of a longitudinally extending, closedpreheating zone having a pair of ends;

introducing hot preheating gases into said one end of the preheatingzone, and moving said gases through lthe preheating zone;

forming, in said preheating zone, a moving suspension of preheatinggases and ore particles;

said ore particles and said hot preheating gases undergoing a mutualheat transfer in said preheating zone to provide heated ore particlesand cooled gases;

and separating the heated ore particles at the other end of thepreheating zone from said cooled gases;

i at least part of the volume of said hot preheating gases beingprovided by circulating gases from said stream of gases at the other endof said reaction zone to the one end of said preheating zone;

recycling at least part of said cooled preheating gases to said streamof gases introduced into the one end of said reaction zone;

and subjecting said recycled cooled preheating gases to at least twostages of separation from said ore material before said recycling ofsaid cooled preheated gases. l

References Cited by the Examiner UNITED STATES PATENTS 2,343,780 3/ 44Lewis 75--26 2,399,984 5/ 46 Caldwell 75-26 2,870,003 1/59 Cavanagh75-26 FOREIGN PATENTS 690,527 4/ 53 Great Britain.

DAVID L. RECK, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE 0E CORRECTION Patent No. 3,190,744 June 22, 1965 Richard E. King It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

Column l, line 54, after "When" insert iron column 4, line 67, for"cycline" read cyclone column 7, line 52, for "or" read ore column 8,line 4l, for "then" read than column 9, line 19, for "relationsihp" readrelationship U column Il, line l0, for "parlicles" read particles line55, before "a" insert at column 13, line 3l, for "second group" readsecond-group Signed and sealed this 21st day of December 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. THE PROCESS OF TREATING A FERRUGINOUS ORE MATERIAL HAVING AT LEAST A PORTION OF ITS IRON CONTEND IN THE FORM OF NON-MAGNETIC OXYGEN-CONTAINING COMPOUNDS REDUCIBLE TO MAGNETITE, SAID PROCESS COMPRISING THE STEPS OF: PROVIDING SAID ORE MATERIAL AS FINELY DIVIDED PARTICLES; PROVIDING A STREAM OF HEATED GASES CONSISTAING ESSENTIALLY OF AT LEAST ONE GAS SELECTED FROM A FIRST GROUP CONSISTING OF CARBON MONOXIDE (CO) AND HYDROGEN (H2) AND AT LEAST ONE GAS SELECTED FROM A SECOND GROUP CONSISTING OF CARBON DIOXIDE (CO2) AND WATER VAPOR (H2O), WITH SAID STREAM OF GASES BEING FREE OF UNCOMBINED OXYGEN AND AT A TEMPERATURE BELOW THE FUSION POINT OF SAID ORE MATERIAL; PROVIDING SAID STREAM OF GASES WITH A RATIO OF FIRSTGROUP SAID ORE MATERIAL AT SAID TEMPERATURE; INTRODUCING SAID STREAM OF GASES INTO ONE END OF A CLOSED, LONGITUDINALLY EXTENDING REACTION ZONE AND MOVING THE STREAM OF GASES THROUGH SAID REACTION ZONE; INTRODUCING SAID PARTICLES OF ORE MATERIAL INTO SAID ONE END OF SAID REACTION ZONE WITH PARTICLES HAVING A DOWNWARD VELOCITY COMPONENT AT THE TIME OF SAID INTRODUCTION; FORMING A FREE SUSPENSION OF SAID PARTICLES IN SAID STREAM OF GASES, WITH SAID SUSPENSION MOVING THROUGH THE REACTION ZONE FROM SAID ONE END TO THE OTHER END THEREOF; REDUCING SAID NON-MAGNETIC OXYGEN-CONTAINING COMPOUNDS IN SAID PARTICLES TO MAGNETITE, DURING MOVEMENT OF THE SUSPENSION THROUGH SAID REACTION ZONE, TO RENDER SAID PARTICLES FMAGNETIC; CONTROLLING THE RATIO OF FIRST-GROUP GASES TO SECOND-GROUP GASES AND THE TEMPERATURE OF SAID STREAM OF GASES IN THE REACTION ZONE TO PREVENT OVER-REDUCTION OF THE ORE PARTICLES TO METALLIC IRON OR TO WUSTITE AND TO MAINTAIN MAGNETITE AT THE OTHER END OF THE REACTION ZONE; SEPARATING SAID ORE PARTICLES AT SAID OTHER END OF THE REACTION ZONE FROM SAID STREAM OF GASES; THE MOVEMENT OF SAID STREAM OF GASES, FROM THE TIME THE ORE PARTICLES BECOME SUSPENDED IN THE STREAM OF GASES UNTIL THE STREAM OF GASES REACHES THE OTHER END OF THE REACTION ZONE, CONSISTING OF MOVEMENT IN A DIRECTION HAVING AN UPWARD COMPONENT; AND MAGNETICALLY SEPARATING THE MAGNETIC PARTICLES FROM THE NON-MAGNETIC PARTICLES IN SAID ORE MATERIAL, WITHOUT FURTHER REDUCTION OF THE ORE MATERIAL. 